Whipstocks are well known devices used in various well operations to deviate one or more well tools from a direction along the long axis of a wellbore. This way the well tools will operate at an angle to the long axis of the wellbore. This is done in order to drill deviated wellbores that extend into the earth at an angle to the long axis of the main or primary wellbore from which the deviated wellbore is drilled.
The standard whipstock is a long tool anywhere from ten to twenty feet or more, which takes the shape of a very long right triangle. The short base of the right triangle is the bottom of the whipstock in the wellbore. An upstanding back surface intersects the base at essentially a right angle. The hypotenuse is the gently sloping guide surface of the whipstock which forces the well tools into a direction which is at an angle to the long axis of the main wellbore.
Normally, when a whipstock is set in a wellbore such as one lined with conventional steel conduit such as casing, the back surface of the whipstock rests in essentially its entirety against the inner wall or surface of the casing. Thus, the whipstock is supported along essentially its entire back surface length by contact with the wellbore or the casing lining same. When the whipstock bottom is set on a rigid anchor or cement plug, the whipstock is well supported over the full length of its bottom surface and its back surface with only the guide surface left unsupported and pointing generally upwardly to receive the impact of downward traveling well tools in order to direct those well tools away from the long axis of the wellbore.
Sometimes the interior of the main wellbore has one or more restrictions along the length thereof which reduce the cross-sectional area of the wellbore. Thus, whatever tool that is passed down the interior of that wellbore has to be small enough in cross-section to pass through those restrictions in order to reach lower levels in the wellbore. There are many restrictions that can be imposed in a wellbore and this invention is applicable to all of them, but for sake of clarity, the only restriction referred to hereinafter will be that of a string of production tubing that is carried concentrically within the main wellbore and that is of a smaller internal diameter than the wellbore itself or any casing lining the wellbore itself. This is called through tubing operations in that any well operations that are to be carried out in the wellbore below the end of the production tubing has to be passed through the interior of the production tubing before it can reach the area where the well operation is to be carried out. Otherwise the production tubing has to be removed in its entirety from the wellbore, which is an expensive and time consuming process. Thus, it is very desirable to be able to pass well tools that are to be used in well operations through the interior of the smaller diameter production tubing down below the end of that tubing into the larger diameter wellbore and then carrying out well operations with those tools in that larger area of the wellbore.
Often times well tools that are made small enough to pass through restrictions such as production tubing do not operate as well in the larger wellbore area below the end of the production tubing and this includes whipstocks. This is so because the small tools do not take up the space afforded by the larger wellbore area, and, therefore, there is more room for operating error such as a mill jumping off the guide surface of a whipstock.
This invention is directed toward a whipstock modified so that it can be passed through one or more restrictions within a wellbore and still operate reliably in the larger diameter area of the wellbore below the end of any such restriction.